Until 1978, hypophyseal alpha MSH was believed to be a monoacetylated peptide with actions on melanocytes, fat cells and brain but without effects on the adrenal cortex. Recent work here has shown that most pituitary alpha MSH is in fact diacetylated and that diacetyl alpha MSH stimulates growth and DNA synthesis in the fetal and adult adrenal cortex. Our objective now is to understand the biosynthesis, secretion and physiologic function of diacetyl alpha MSH.